any java coders? or c++ ?

this should be easy for you but im getting stumped.

(a) Create a Java class PositionPair, with instance fields private int firstOccurrence = -1 and private int secondOccurrence = -1. Use the Eclipse tool Source->Generate Getters and Setters to write the get and set methods for these fields.

(b) In your main class, write a method that contains an array PositionPair[] positions = new PositionPair[10]. Loop through all of digitArray. The first time you see the digit d in digitArray, store the index in positions[d].firstOccurrence and the second time, store the index in positions[d].secondOccurrence. When you are done, find the minimum value of all the firstOccurrences, that are positive, where the corresponding secondOccurrence is not -1. Return that minimum firstOccurrence as the return value of the method.

I cant get it working..
so far my code is

code:


package homework6;

public class PositionPair
{
	private int firstOccurence = -1;

	private int secondOccurence = -1;

	public int getFirstOccurence()
	{
		return firstOccurence;
	}

	public void setFirstOccurence(int firstOccurence)
	{
		this.firstOccurence = firstOccurence;
	}

	public int getSecondOccurence()
	{
		return secondOccurence;
	}

	public void setSecondOccurence(int secondOccurence)
	{
		this.secondOccurence = secondOccurence;
	}
	

	public static int Fuck(int[] digitArray)
	{
		PositionPair[] positions = new PositionPair[10];
		int i = 0;
		int z = 0;
		for (i = 0; i < digitArray.length; i++)
			{
				for (z = i + 1; z < digitArray.length; z++)
				{
					if (digitArray[z] == digitArray[i])
					{	
						positions[i].firstOccurence = i;
						positions[i].secondOccurence = z;
						
					}
					
				}
			
		}
		//return something
		
	}

I found something odd:

quote:

Originally posted by stan229 (b) In your main class, write a method that contains an array PositionPair[] positions = new PositionPair[10].

You were told to do this in your main class, not in the PositionPair class as it is. It seems odd to create an array of PositionPairs in a method part of a single PositionPair object.

Also, shouldn't this part:

code:
if (digitArray[z] == digitArray[i])

code:
if (digitArray[z] == i)

I think that's the problem with filling out the "positions" array, after it has been filled it should be easy to return the wanted value.

Try drawing a bunch of arrays in a sheet of paper and filling them out by yourself as you simulate the program running in your head. I ocasionally do that and it helps. Or you could just debug.

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Posted by stan229 on Oct-10-2006 02:13:

then i woudlnt be able to access firstOccurence cuz its private
unless theres another way?

also changin the thing to digitArray[z] == i doesn change anything, and im using that just to test if the value is repeated

the error i get is:

code:

Exception in thread "main" java.lang.NullPointerException
	at homework6.PositionPair.Fuck(PositionPair.java:41)
	at homework6.PositionPair.main(PositionPair.java:56)

yea so i modified the code.. had to create a ne class
i used your advice on the method so i have

code:
 int[] digitArray =
		{ 0, 1, 1, 3, 4, 5, 5, 7, 8, 9 };

		PositionPair[] positions = new PositionPair[10];
		for (int i = 0; i < digitArray.length; i++)
		{
			for (int z = i + 1; z < digitArray.length; z++)
			{
				if (digitArray[z] == digitArray[i])
				{
					positions[i].setFirstOccurence(i);
					positions[i].setSecondOccurence(z);
					System.out.println(i);
					System.out.println(z);
				}

			}

		}

tried a simple test and still got a nullPointerException..hmm

code:

		positions[0].setFirstOccurence(5);
		System.out.println(positions[0].getFirstOccurence());

Firstly, where's your default constructor for the PositionPair Class? cause at the moment you cant even create one of these objects right? So make one of those.

code:

public PostionPair()
{
   firstOccurence = -1;
   secondOccurence = -1;
}

code:

PositionPair[] positions = new PositionPair[10];

code:

for(int a = 0; a < 10; a++)
{
   positions[a] = new PositionPair(); //You'll need a default  constructor for this!
}

code:

int[] digitArray = { 0, 1, 1, 3, 4, 5, 5, 7, 8, 9 };

		PositionPair[] positions = new PositionPair[10];
                
                //ADDED CODE
                for(int a = 0; a < 10; a++)
                {
                   positions[a] = new PositionPair(); //You'll need a default constructor for this!
                }

		for (int i = 0; i < digitArray.length; i++)
		{
			for (int z = i + 1; z < digitArray.length; z++)
			{
				if (digitArray[z] == digitArray[i])
				{
					positions[i].setFirstOccurence(i);
					positions[i].setSecondOccurence(z);
					System.out.println(i);
					System.out.println(z);
				}

			}

		}

thanks for everyones help i appreciate it.. lol i did
heres the final working code:

code:

// Sorry that I put everything in the test class.
//I realized to change it in the last minute and don't have time to, code will still work though.

package homework6;

public class PositionTest
{
	/**
	 * Find the minimum index for firstOccurence
	 * 
	 * @param positions
	 * @return index
	 */
	public static int findMinimum(PositionPair[] positions)

	{
		if (positions.length == 0)
			return -1;
		int smallestVal = -1;

		for (int i = 0; i < positions.length; i++)
		{
			if (positions[i].getSecondOccurence() != -1
					&& (positions[i].getFirstOccurence() < smallestVal || smallestVal == -1))
				smallestVal = positions[i].getFirstOccurence();

		}
		return smallestVal;
	}

	public static void main(String[] args)
	{

		int[] digitArray =
		{ 0, 1, 2, 1, 2, 5, 5, 7, 8, 9 };

		PositionPair[] positions = new PositionPair[10];
		for (int i = 0; i < positions.length; i++)
			positions[i] = new PositionPair();

		// Loop to test for firstOccurence and secondOccurence
		for (int i = 0; i < digitArray.length; i++)
		{
			if (positions[digitArray[i]].getFirstOccurence() == -1)
			{
				positions[digitArray[i]].setFirstOccurence(i);
			} else if (positions[digitArray[i]].getSecondOccurence() == -1)
			{
				positions[digitArray[i]].setSecondOccurence(i);
			}
		}

		// Prints out array
		for (int i = 0; i < positions.length; i++)
		{
			System.out.println(positions[i].getFirstOccurence() + " "
					+ positions[i].getSecondOccurence());

		}

		int n = findMinimum(positions);
		System.out.println(n);

	}
}

code:

package homework6;

public class PositionPair
{
	private int firstOccurence = -1;

	private int secondOccurence = -1;

	public int getFirstOccurence()
	{
		return firstOccurence;
	}

	public void setFirstOccurence(int firstOccurence)
	{
		this.firstOccurence = firstOccurence;
	}

	public int getSecondOccurence()
	{
		return secondOccurence;
	}

	public void setSecondOccurence(int secondOccurence)
	{
		this.secondOccurence = secondOccurence;
	}
	

}

Once again, thank you guys. I was up till very late in the morning working on this that day.

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